It's a 42mm case, same as the old, big Super Compressors and reissues like the Polaris and, I presume, the Aquatimer Vintage. I'm hoping someone reps the Super Compressor case, since there are so many great divers that used it. At the very least, a Polaris rep would be nice, as I doubt I'll be able to afford one anytime soon!
Here's a nice side-by-side from someone who owns the old and new Divers:
If only IWC had been as faithful to the ref.1812 Aquatimer as JLC and Longines were to their old divers! Aside from the lack of a Plexiglas dome, Longines' only other noticeable deviation from the original is the hands: The hour hand is fine, but the minute hand is too straight and narrow, and the second hand is too thick. Oddly, all the official photos of the LLD show the old-style hands, yet every purchased example I've seen has hands like those on mine.